1. Field of the Invention
The present invention relates generally to an improved integrated circuit design system, and in particular, to a method for modifying an integrated circuit design for manufacture. Still more particularly, the present invention relates to a method, system, and computer usable program code for fracturing a high resolution or continuous mask for improved manufacturability using photolithography.
2. Description of the Related Art
Modern day electronics include components that use integrated circuits (ICs). Integrated circuits are electronic circuits formed using semiconductor substrates and by adding impurities to form solid-state electronic devices, such as transistors, diodes, and resistors. Commonly known as a “chip”, an integrated circuit is generally encased in hard plastic. The components in modern day electronics generally appear to be rectangular black plastic pellets with connector pins protruding from the plastic encasement.
Circuit designers use a variety of software tools to design and test electronic circuits that accomplish an intended task. For example, a digital circuit may be designed to accept digital inputs, perform some computation, and produce a digital output. An analog circuit may be designed to accept analog signals, manipulate the analog signals, such as my amplifying, filtering, or mixing the signals, and produce an analog or digital output. Generally, any type of circuit can be designed as an IC.
Once a design layout, also referred to simply as a layout, has been finalized for an IC, the design is converted into a set of masks or reticles. A set of masks or reticles is one or more masks or reticles. During manufacture, a semiconductor wafer is exposed to light or radiation through a mask to form microscopic components of the IC. This process is known as photolithography.
A layout includes shapes that the designer selects and positions to achieve a design objective. Through a process known as optical proximity correction (OPC), the shapes are transformed in a mask to correct for optical and other manufacturing related idiosyncrasies. This is generally done by counterbiasing the mask at each of a number of segments along the edges of the mask shapes. These segments are also known as fragments. A mask may make use of shapes that include continuous curves. An optical proximity corrected (OPC'd) mask rarely includes continuous curves.
Inverse lithography, also known as Inverse Lithography Technology (ILT), is a technique where a shape is adjusted on a mask or a portion or region of a mask using methods of numerical optimization as opposed to manipulating a shape by simple counter-biasing to correct the bias introduced by idiosyncrasies of the manufacturing process. Inverse lithography masks often include continuous curves and shapes. A continuous curve is a smooth form curve including no sharp angle or intersection of lines or curves. A continuous shape is a shape comprising a continuous curve, including a closed continuous curve.
Source Mask Optimization (SMO) is a technique where mask shapes on a mask or portion of a mask are adjusted along with the light illuminating the mask using methods of numerical optimization. SMO masks may include continuous curves and shapes.
Techniques such as OPC, ILT, and SMO usually require the calculation of intensities produced on the semiconductor wafer when the mask is illuminated. Techniques for calculating these intensities are well-known, for example by means of convolution of the mask with so-called SOCS kernels.
A high resolution mask includes shapes at such a scale that the boundary of a shape appears as a continuous curve at manufacturing resolution. In other words, even if a shape includes rectangular patterns, the size and proximity of those rectangular patterns make the shape appear as a continuous shape on a manufacturing mask. Manufacturing resolution can be considered either a resolution in terms of distance between points that can be printed on a wafer using a photolithography mask, or it may be considered a resolution in terms of distance between patterns that can be fabricated on a mask with available mask making processes. High resolution is a resolution higher than manufacturing resolution. A manufacturing mask is a mask usable for successfully manufacturing or printing the contents of the mask onto wafer.